This invention relates to internal combustion engines and more particularly to systems and method for providing speed limit control in such systems.
As is known in the art, it is sometimes desirable to provide speed limit control in internal combustion engines. One such application for such a speed limit control is in engine systems having electronic throttle control (ETC).
As is also known in the art, some internal combustion engines having ETC use a torque monitoring function. This function checks the desired engine torque, (i.e., driver demanded torque from, for example, a sensing of driver accelerator pedal position) with two independent measures of torque, for example, a throttle based (e.g., throttle position) estimate and an air-meter (i.e., Mass Air Flow, MAF) based method. If there is a loss of a throttle position signal, or MAF signal, for example, conditions warrant going into an ETC Alternative Management (AM) mode. In such AM mode, the powertrain is no longer be controlled based on torque but rather monitored engine speed. If engine speed is xe2x80x9ctoo highxe2x80x9d (i.e., above an allowable limit), all fuel injectors are disabled so that there is no torque produced by the engine. If fuel injector activity is observed when engine speed is above the allowable limit, the system transitions to a shutdown mode; i.e., fuel injection and electronic throttle control are permanently disabled.
The allowable limit for engine speed is hereinafter sometimes referred to as an RPM limit. The RPM limit is based on the driver""s accelerator pedal position such that if the driver is not depressing the accelerator pedal, the engine speed is kept low (around 1000 to 1200 rpm) to limit wheel torque and creep. When the driver depresses the accelerator pedal, higher engine speed is allowed because the driver is demanding more power. To avoid monitor intervention that would put the system in shutdown, the main control system controls engine speed and the fuel injectors to satisfy the above-described criteria and thus allow continued operation.
Disabling all fuel injectors until engine speed drops below the RPM limit presents a control design challenge (i.e., in preventing the engine from stalling until such time as fuel injection can be resumed) because the load on the engine may be significant and engine speed may drop very rapidly.
In accordance with the invention, a method and system are provided for controlling an internal combustion engine, such engine being coupled to a transmission. The engine is controlled in response to a torque command fed to a controller for controlling such engine. The method includes calculating a torque, tq_tx, on the engine from the transmission, and initializing and/or limiting a torque command to such controller as a function of the calculated torque, tq_tx.
In accordance with another feature of the invention, a method and system are provided for controlling engine speed. The system and method determine a range of allowable engine speeds, such range extending from a low limit, LOW_LIM=cnt_n_limxe2x88x92K1 to a high limit, LIM_HIGH=cnt_n_lim+K2, where K1 and K2 are predetermined constants, and cnt_n_lim is a function of operator input. An error, n_error, between measured engine speed and ctrl_n_lim is calculated. The error is fed to a feedback controller. The controller produces an engine brake torque, tqe_rpm, command for the engine. The controller disables engine fuel injection when the measured engine speed is greater than LIM_HIGH and enables fuel injection if the measured speed is within the range.
In one embodiment, a torque, tq_tx, on the engine from a transmission coupled to the engine is calculated. When measured engine speed decreases from a speed greater than LIM_HIGH, wherein fuel injection was disabled, to within the range, the controller enables fuel injection and provides, as an initial value for the engine brake command torque, the calculated torque, tq_tx.
In one embodiment, the controller provides proportional plus integral control action of the error, and wherein the integral action is initialized with the calculated torque to provide the initial value for the engine command torque.
In accordance with another feature of the invention, a method and system are provided for controlling engine speed. The system and method determine a range of allowable engine speeds, such range extending from a low limit, LOW_LIM=cnt_n_limxe2x88x92K1 to a high limit, LIM_HIGH=cnt_n_lim+K2, where K1 and K2 are predetermined constants, and cnt_n_lim is a function of operator input. An error, n_error, between measured engine speed and ctrl_n_lim is calculated. The error is fed to a feedback controller. The controller produces an engine brake torque, tqe_rpm, command for the engine. The controller disables engine fuel injection when the measured engine speed is greater than LIM_HIGH and enables fuel injection if the measured speed is within the range. A torque load, tq_tx, on the engine is calculated from a transmission coupled to the engine. A determination is made as to whether measured engine speed is a potential stall speed. If measured engine speed is within the range and such measured engine speed is a potential stall speed, the controller operates to maintain tq_tx as the engine brake torque command to the engine.
In one embodiment, the controller provides proportional plus integral control action on the error, and wherein the integral action is clipped to maintain at least tq_tx as the engine brake torque command to the engine.
In accordance with still another feature of the invention, a method and system are provided for controlling engine speed. The system and method determine a range of allowable engine speeds, such range extending from a low limit, LOW_LIM=cnt_n_limxe2x88x92K1 to a high limit, LIM_HIGH=cnt_n_lim+K2, where K1 and K2 are predetermined constants, and cnt_n_lim is a function of operator input. An error, n_error, between measured engine speed and ctrl_n_lim is calculated. The error is fed to a feedback controller. The controller produces an engine brake torque, tqe_rpm, command for the engine. The controller disables engine fuel injection when the measured engine speed is greater than LIM_HIGH and enables fuel injection if the measured speed is within the range. A torque load, tq_tx, on the engine from a transmission coupled to the engine is calculated. A determination is made as to whether measured engine speed is a potential stall speed. If measured engine speed is greater than a potential stall speed, and if the fuel injection was not disabled, having the controller operate to provide proportional plus integral operation on the error in providing the engine brake torque command to the engine.
In accordance with still another feature of the invention, a controller is provided to control engine speed to satisfy the RPM guard monitor requirements and provide acceptable engine speed control. More particularly, the controller determines an allowed maximum engine speed, (i.e., an RPM limit (variable ctrl_n_lim)), as a function of: accelerator pedal position. The controller calculates torque (tq_tx) on the engine from the automatic transmission, if present, based on a model of engine torque converter and transmission pump. The controller calculates an error (n13 error), between current engine speed and the allowed maximum engine speed, ctrl13 n_lim. The controller calculates desired engine brake torque (tqe_rpm) based on the error n_error and a set of logic that includes a proportional plus integral (PI) controller. The controller translates the desired engine brake torque (tqe_rpm) into torque reduction actions by retarding spark, cutting out injectors and using lean air-fuel ratios.
Thus, torque-based controller output (tqe_rpm) is used to disable all fuel injection until engine speed drops below the RPM guard limit while feedforward transmission torque calculations and other logic are used to prevent the engine from stalling until such time when fuel injection can be resumed.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.